BaSrTiO3/YIG microwave phase shifter with large two-degree-of-freedom tuning

Ferroelectric material Ba_0.5Sr_0.5TiO₃ has been grown on a polycrystalline ferrite yttrium iron garnet (YIG) substrate to achieve independent tuning of permittivity and permeability through the electric and magnetic field, respectively. A large dielectric constant and dielectric-constant tuning of the BST layer has been achieved with a simple deposition procedure by RF magnetron sputtering. Coplanar waveguides were fabricated on the bilayer structure to demonstrate the benefits of additional permeability tuning by external applied magnetic field: (i) to alleviate the impedance-mismatch caused by electric-field tuning of permittivity; (ii) to improve differential phase shift. A large differential phase shift of 77°/cm at 5°GHz for an applied electric field of 60°kV/cm has been achieved with the aid of the magnetic field.